1. Field of the Invention
This invention relates to an impulse sensor for sensing an impulse.
2. Description of the Related Art
As a conventional impulse sensor, there is an impulse sensor using a cable. This impulse sensor is characterized in that an impulse can be sensed in an entire longitudinal direction of the cable. There are cable sensors of a type using an optical fiber in which propagation light is varied by deformation of the optical fiber, of a type using a cable in which electric potential is varied by pressure, of a type using pressure-sensitive rubber in which electric resistance is varied by pressure, and of a type using longitudinally arranged switches which are turned ON/OFF by an impulse.
The impulse sensor using an optical fiber is caused to sense an impulse by applying, to an optical fiber made of quartz glass or synthetic resin, an impulse, such as pressure, acceleration or strain, causing bend loss and compression loss of the optical fiber, and thereby varying propagation light quantity in the optical fiber (See JP-A-9-26370 and JP-A-2002-531812, for example).
In the field of automobiles and traffic, it is important to quantitatively know automobile collision from the points of view of drivers' safety and pedestrian protection, and the application of the impulse sensors to this field is therefore studied. For example, installing the impulse sensor along a bumper allows sensing an impulse received by the bumper due to vehicle collision.
In the impulse sensor installed along the bumper, there is the problem that an output value of the impulse sensor varies according to portions of the vehicle for the same collision load.
Two reasons considered for this are because of differences in impulse transmission from the bumper to the impulse sensor due to rigidity of the bumper varying according to thickness and structure differences in portions of the bumper in the vehicle width direction, and because of differences in load applied to the impulse sensor due to angle differences between the middle and both right and left ends of the bumper relative to a direction of an impulse received by the bumper.